1. Field of the Invention
This invention relates to a speed control system for controlling the speed of a turbine by modulating the position of a servomotor throttle valve disposed between the turbine and a stream source for controlling the admission of steam to the turbine, and more particularly, to a microprocessor-based control system incorporating a plurality of permanently pre-programmed read-only-memories which characterize the operation of the speed control system.
2. Prior Art Discussion
Recently, general purpose minicomputer systems have been developed for the purposes of controlling the speed and load of a steam turbine. Minicomputer-based turbine controllers, similar to that described in the U.S. application, Ser. No. 722,799 (abandoned), entitled "Improved System And Method For Operating A Steam Turbine And Electric Power Generating Plant"; filed by Giras and Birnbaum on Apr. 4, 1968 and continued as Ser. No. 124,993 on Mar. 16, 1971 and Ser. No. 319,115 (abandoned) on Dec. 29, 1972 and Ser. No. 720,725 on Sept. 7, 1976, permitted turbine control operation to be characterized by a set of programs. Quite a few large turbine systems could justify the expense of a general purpose, minicomputer-based turbine controller because of the added features of automatic start-up, synchronization and automatic efficient load control afforded thereby. However, some municipalities and industrial complexes employ smaller turbines, on the order of 300 megawatts of less, which incorporate simple steam admission control valving arrangements usually actuated by mechanical-hydraulic servomotors as opposed to the large turbines, say 1,000 megawatts or greater, which use a variety of complex electrohydraulic actuated valving arrangements. These smaller turbines have generally been controlled by an operator using a basic fixed hardwired digital speed controller such as that described in U.S. Pat. No. 3,802,188; by Barrett, issued Apr. 9, 1974. In these cases, the operator performs the protective control of the turbine, manually, according to a set of operational limitations provided to him by the turbine manufacturer.
Presently, there exists some controversy surrounding the effectiveness of using a general purpose minicomputer-based machine for controlling small turbines, particularly where only a single loop speed control function is required. Normally, each general purpose minicomputer incorporates a number of system software type programs for coordinating the operation of the circuitry associated therewith. In order to apply a minicomputer to a specific function, one must, for the most part, be fully knowledgeable of the "operating systems" software package corresponding thereto. These "operating systems" dictate the priority structuring and arrangement of the sets of instructions and data programmed therein for the purposes relating to steam turbine speed control applications, for example.
Programs associated with both application and circuit operation are generally stored on rolls of punched paper tape prior to being entered into the minicomputer system. The order in which programs are entered into the read/write memory of the minicomputer system is performed in accordance with the specific system program generation procedures outlined by the "operating system" corresponding to the minicomputer used. Accordingly, additional peripheral equipment, non-essential to the control of the process, such as a tape punch, a tape reader and a teletypewriter are generally needed to ensure that proper program loading techniques have been instituted and that the programs have been assigned to the correct memory areas as a result of the loading process. It has become necessary then to not only be knowledgeable about the process that is to be controlled, but to also become equally knowledgeable about the complexities involved in loading the programs into the minicomputer systems being used in accordance with the procedures of its "operating system".
Present minicomputer systems also involve read/write memory which is susceptible to electrical noise "spikes" which occur frequently in power plant environments. Frequent occurrences of these "spikes" may cause a change in an instruction in the read/write memory which could be responsible for an eventual shutdown of the turbine process.